The parietal eye of lizards is a photosensitive organ located on the dorsal midline o the animal. Its photoreceptors synapse directly onto ganglion cells, but afferent signal flow is additionally modified by centrifugal input. It is proposed to define the receptive fields and light-evoked responses of both classes of intrinsic neurons through single-cell recordings. Morphological studies employing a variety of light microscopic and electron microscopic techniques will be utilized to characterize the neuronal geometry, synapses and central connections of the parietal eye.